Fastest way to search a number in a list of ranges

Question

I have the following code to find a match for a number in a list of ranges.

public class RangeGroup
{
    public uint RangeGroupId { get; set; }
    public u         


        

Answer 1

Since you indicated that RangeGroups are added in order of RangeGroup.Low and that they do not overlap, you don't need to do any further pre-processing. You can do binary search on the RangeGroups list to find the range (warning: not fully tested, you'd need to check some edge conditions):

public static RangeGroup Find(uint number) {
    int position = RangeGroups.Count / 2;
    int stepSize = position / 2;

    while (true) {
        if (stepSize == 0) {
            // Couldn't find it.
            return null;
        }

        if (RangeGroups[position].High < number) {
            // Search down.
            position -= stepSize;

        } else if (RangeGroups[position].Low > number) {
            // Search up.
            position += stepSize;

        } else {
            // Found it!
            return RangeGroups[position];
        }

        stepSize /= 2;
    }
}

The worst-case run time should be around O(log(N)), where N is the number of RangeGroups.